The invention relates to a wafer lifting device having a lifting platform arranged under a wafer support member, the top side of which forms a wafer bearing area, wherein the lifting platform can be moved toward and away from the underside of the wafer support member, in a vertical direction. At least three pins extending in the vertical direction are arranged to move in through holes in the wafer support member, which run from the underside of the wafer support member to the wafer bearing area on the top side thereof. With the lifting platform raised, in a first upper position near the underside of the wafer support member, the pins project from the wafer bearing area by a selected amount. With the lifting platform lowered, in a second lower position remote from the underside of the wafer support member, the pins are retracted into the support member.
It is known that, for fabricating semiconductor components with a wide variety of functions, chips are subjected to a plurality of process steps in which the semiconductor material undergoes various physical-chemical treatments.
During some of these process steps and also during the testing of chips in the wafer composite, the wafers are placed on wafer support members and treated in a horizontal position. There are provided handling systems which take up the wafers, position them over the wafer support member and deposit them on the wafer support member by means of a vertical relative movement between wafer support member and handling system.
The wafer support member may be designed as a heating plate. In particular, such heating plates are used during the process step of resist incineration. During this process step, the wafers are heated by means of the heating plate, and the hot wafers are exposed to an oxygen atmosphere. As a result, the photoresist of a photoresist mask which is situated on the wafer oxidizes to form a volatile gas and burns without any residue.
Such wafer support members designed as heating plates are provided with a wafer lifting device. The wafer lifting device comprises a lifting platform arranged under the heating plate, which lifting platform can be moved vertically by means of a pneumatic cylinder, whereas the wafer support member is fixed. Three vertical pins which project into holes in the heating plate are fastened on the lifting platform. The holes are designed as through holes and accordingly extend from the underside of the heating plate as far as its top side, serving as wafer bearing area. The pins have a length such that they project from the wafer bearing area by a selected amount with the lifting platform raised. With the lifting platform lowered, the pins are sunk in the holes. During a lifting movement of the lifting platform, the pins are guided in the through holes.
If a wafer is then to be deposited onto the heating plate, firstly the lifting platform is moved into its upper position, the pins projecting from the wafer bearing area. By means of a handling device having a supporting fork, on which the wafer is carried, the wafer is brought over the heating plate and moved downward. In this case, the wafer is deposited on the pins and the supporting fork is relieved of the burden of the wafer and can then be retracted from the space between wafer underside and wafer bearing area. The lifting platform is subsequently lowered until the top ends of the pins lie in the through holes. As a result, the wafer is deposited on wafer bearing area.
If the wafer is to be removed again after the corresponding process step, the procedure is reversed.
Since the pins become heated during processing of a wafer, when the wafer is placed onto the pins, it is heated by the pins in point-type fashion. However, such point-type exposure of the wafer to heat is unfavorable for technological reasons. For this reason, the pins are provided with tips at their top side in order to minimize the heat dissipation.
Such a wafer lifting device has the disadvantage that the pins cannot be guaranteed to be guided entirely satisfactorily on account of the thermal expansion between the through holes. This has the effect that the pins may rub in the through holes, which leads firstly to an extremely undesirable generation of particles on account of a material removal in the through holes or at the pins, and secondly to a scratching of the wafers on the underside. In the case of scratching of the wafers, particles may then in turn be produced and, moreover, the risk of the wafer breaking may be increased.
Consequently, the invention is based on the object of configuring the guide of the pins in the through holes to avoid any disadvantageous effects for the process sequence.